In many modern electronics applications, it is desirable to convert an analog signal to a digital value. For example, in a radio frequency (RF) transceiver, a received analog RF signal may be demodulated to an analog baseband signal which is then converted to a digital baseband signal for subsequent digital signal processing. In some applications, voltage-controlled oscillator (VCO) quantizers are used to convert an analog signal to a digital representation. In a VCO quantizer, an analog input signal controls the oscillation frequency of a VCO, where the oscillation frequency is proportionally related to the magnitude of the analog input signal. The number of oscillations within the sampling period are counted, resulting in a digital value that corresponds to the magnitude of the analog input signal.
Many VCOs in VCO quantizers consist of an odd number of delay stages (or delay cells) configured as a ring oscillator. In some prior art systems, the number of delay stages correspond to the number of quantization levels achievable by the VCO quantizer. Each delay stage is often realized as a complementary metal-oxide-semiconductor (CMOS) inverter (or NOT logic gate). However, in order to achieve high linearity and satisfy other performance metrics, in practice, the CMOS inverters are realized as specialized semiconductor devices that consume substantially more area and power than the other elements of the VCO quantizer when the VCO quantizer is implemented in circuitry.